Ski with microporous bottom surface

ABSTRACT

A ski including an elongated relatively narrow strip having a normally upwardly directed surface to be engaged by a ski boot and a normally downwardly directed opposed surface, the ski including a bottom layer which is fixed to the strip and engages and covers the opposed surface thereof, this bottom layer being composed for the most part of a plastic in which hollow tubular fibers are embedded with some of the fibers being exposed at a surface of the bottom layer which is directed away from the strip to provide the latter surface of the bottom layer with a microporous structure. During manufacture the bottom layer composed for the most part of plastic in which the hollow tubular fibers are embedded is applied to the bottom surface of the strip and while being pressed against the bottom surface of the strip is cured to form a plate fixed to the bottom surface of the strip. The bottom layer is then ground at its surface which is directed away from the strip to expose fibers at the ground surface, thus giving the latter surface a microporous structure.

United States Patent 1 1 Tiitola 1 July 29, 1975 1 SKI WITH MICROPOROUSBOTTOM SURFACE [75] Inventor: Antti-JussiTiitoIa,Tampere,

Finland [73] Assignee: Karhu-Titan 0y, Helsinki, Finland [22] Filed:Feb. 22, 1974 [2]] Appl. No.: 444,876

Primary Examiner-Kenneth H. Betts Assistant Examiner David M. MitchellAttorney, Agent, or FirmSteinberg and Blake [57] ABSTRACT A skiincluding an elongated relatively narrow strip having a normallyupwardly directed surface to be engaged by a ski boot and a normallydownwardly directed opposed surface, the ski including a bottom layerwhich is fixed to the strip and engages and covers the opposed surfacethereof, this bottom layer being composed for the most part of a plasticin which hollow tubular fibers are embedded with some of the fibersbeing exposed at a surface of the bottom layer which is directed awayfrom the strip to provide the latter surface of the bottom layer with amicroporous structure. During manufacture the bottom layer composed forthe most part of plastic in which the hollow tubular fibers are embeddedis applied to the bottom surface of the strip and while being pressedagainst the bottom surface of the strip is cured to form a plate fixedto the bottom surface of the strip. The bottom layer is then ground atits surface which is directed away from the strip to expose fibers atthe ground surface, thus giving the latter surface a microporousstructure.

9 Claims, 4 Drawing Figures PATENTEDJUL29975 Fl G. 1

FIG. 3

SKI WITH MICROPOROUS BOTTOM SURFACE BACKGROUND OF THE INVENTION Thepresent invention relates to skis.

In particular, the present invention relates to skis having bottomstructures for providing the skis with desired sliding properties, aswell as to methods for manufacturing such skis.

It is known to provide for skis different types of synthetic materialssituated at the bottom sliding surfaces of the skis. Sliding bottomsurfaces of skis have been manufactured from thermosetting as well asthermoplastic materials. Thus, polyethylene is one of the thermoplasticmaterials most frequently used for this purpose and has indeed beenfound to be extremely good for alpine skiing. However, the use of abottom layer of polyethylene for skis intended for cross-country skiingis restricted by reason of the fact that polyethylene has a lowcoefficient of friction at rest, so that skis provided with polyethyleneat the bottom thereof slide very easily and in addition have a pooradherence with wax, so that both from the standpoint of waxing as wellas of cross-country skiing polyethylene is undesirable. Other materialshaving characteristics similar to those of polyethylene have been used,such as Teflon and polypropylene, but there has been no general use ofthese thermoplastic materials.

Skis with bottom layers consisting exclusively of thermosetting plastichave not been in use unless it is considered that a polyester andepoxy-based varnish forms a thermosetting plastic bottom layer. Suchvarnishes have been used in order to increase the wear resistance of thebottoms of Wooden skis. These varnishes have been used in the form ofthin coats having a thickness of less than 0.1 mm, because thermosettingplastics in thicker layers without fillers have too great a tendency toflake off, particularly along the edges of the ski bottom.

A known ski bottom based on a thermosetting plastic is the so-calledplastic wood developed in Finland. This type of construction is believedto be the commonest plastic ski bottom material for skis which at thepresent time are intended for cross-country skiing. The drawback ofplastic wood has proved to be its brittleness, or, in other words, itspoor flexural strength. This latter drawback results from thenon-uniform fibrous structure of the wood as well as its low ductilityacross the grain. These factors result in a tendency of skis havingplastic wood bottoms to break in two, and such skis are easilyscratched, for example by stones.

Another type of known ski bottom includes a combination of thermosettingplastic and a textile fabric having a pile, as disclosed in Finnish Pat.No. 43,401. This ski bottom has an oriented, microscopic pile surfaceprojecting from the ground bottom surface of the ski, and thisconstruction has proved to have a distinct mechanical effect on thesliding and gripping characteristics of the ski. Although such aconstruction has indeed proved to be highly desirable with regard to itsproperties, nevertheless due to the high price of such construction,resulting from the difficulty in manufacturing the ski with the specialfabric, the use of this type of ski has been restricted only to the mostexpensive skis.

Also, as a known material for the bottom of the ski paper laminateimpregnated with phenolic resin has been tried. However, such aconstruction has proved to have an excessive tendency for flaking off.In addition this construction has the drawback of poor adherence withski wax and a poor gliding at low temperatures.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent in vention to provide a ski and a ski-manufacturing method whichwill avoid the above drawbacks.

Thus, it is an object of the present invention to provide a relativelyinexpensive ski having at its bottom a construction which is greatlyimproved as compared to known skis of similar cost.

In addition it is an object of the present invention to provide a skiand ski-manufacturing method according to which it is possible to takeinto consideration the desired use of the ski so that in accordance withthe invention it is possible to provide skis having extremely goodslidability to be used in ski contests, while if desired it is alsopossible to design the ski to have maximum wear resistance for alpineskiing, or it is also possible to provide a ski which has the bestpossible properties for cross-country skiing.

In addition it is an object of the invention to provide a ski with abottom layer having a relatively low thermal conductivity to improve thegliding of the ski on extremely cold snow.

In accordance with the invention the ski includes an elongated ski striphaving a normally upwardly directed surface to be engaged by a ski bootand a normally downwardly directed surface which is engaged and coveredby a bottom layer which is fixed to the ski strip. This bottom layer inaccordance with the present invention is composed for the most part of aplastic in which hollow tubular fibers are embedded. These fibers haveinternal capillary passages, and some of the fibers are exposed andflush with a bottom surface of the bottom layer which is directeddownwardly away from the ski strip, so that in this way this latterbottom surface has a microporous construction. According to the methodof the invention the plastic with the tubular fibers embedded therein isapplied to the bottom surface of the ski strip while being pressedagainst the ski strip during curing so as to form a plate which is fixedto the ski strip, and thereafter the bottom surface of this cured layerwhich is directed away from the ski strip is ground so as to exposefibers at the bottom surface of the bottom layer.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. 1 is a schematic side elevation of a ski according to theinvention;

FIG. 2 is a fragmentary longitudinal sectional elevation of part of theski of FIG. 1 at the region of its lower surface, illustratingschematically the construction of the ski at an enlarged scale;

FIG. 3 is a fragmentary longitudinal sectional eleva tion of the ski atthe region of its lower surface shown at a scale which is much largerthan that of FIG. 2 so as to illustrate in detail the construction ofthe ski; and

FIG. 4 is a fragmentary bottom plan view of the ski of FIG. 1 showingschematically at an enlarged scale the microporous structure of thebottom surface of the ski.

DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with the inventionthe ski has a bottom layer which is designed to slide and which iscomposed for the most part of a thermosetting plastic and a fibrousmaterial in the form of hollow tubular fibers which are embedded in thethermosetting plastic, this plastic with the fibers therein being curedto form a plate which is attached to the bottom of the ski. After curingis completed the exposed bottom surface of the layer of plastic with thetubular fibers embedded therein is machined, as by being ground, so thatthe capillary passages in those fibers which become exposed by grindingat the bottom surface of the bottom layer are opened to provide thebottom surface of the ski with a microporous construction.

Referring to FIG. 1, there is shown therein in a schematic sideelevation a ski strip in the form of an elongated narrow strip of wood,for example, having a normally upwardly directed surface 12 to beengaged by a ski boot. Thus, FIG. 1 schematically illustrates thestructure 14 for releasably holding a ski boot. As may be seen from FIG.1, the strip 10 has fixed thereto a bottom layer 16 which is constructedin accordance with the present invention, the thickness of the bottomlayer 16 being exaggerated with respect to the illustrated thickness ofthe strip 10 in FIG. 1 for the sake of clarity.

Referring to FIG. 2 it will be seen that the strip 10 has fixed theretothe bottom layer 16 which is composed of a synthetic plastic material 18in which hollow tubular fibers 20 are embedded, as schematicallyillustrated. Preferably the plastic 18 is a thermosetting plastic andthe fibers 20 are cellulose fibers. The layer 16 which is composed ofthe most part of the thermosetting plastic 18 and the tubular fibers 20is applied to the bottom surface of the strip 10 and is cured underpressure so that the layer 16 forms a plate which is fixed to the bottomsurface of the strip 10. Then the bottom surface 22 of the layer 16 ismachined as by grinding so as to expose a number of the fibers 20 whichare flush with the bottom surface 22, thus opening the capillarypassages of the fibers 20.

Referring to FIG. 3, which shows this construction at a greatly enlargedscale, it will be seen that one of the fibers 20 has its capillarypassage 24 open at the bottom surface 22 of the plastic material 18.

Referring to FIG. 4 which also shows the construction at an enlargedscale for the sake of clarity, this structure of the invention providesthe bottom surface 22 of the ski with a multiplicity of tiny openings 26which give the bottom surface a highly desirable microporousconstruction.

Thus, with the present invention the bottom layer of the ski willeliminate all of the drawbacks which have been encountered with plasticwood while at the same time preserving properties which are importantwith respect to good gliding of the ski and the capability of waxing thebottom thereof. By selecting for the material to be impregnated with thethermosetting plastic 18, instead of wood, hollow tubular fibers 20which preferably are cellulose fibers or other equivalent tubular hollowfibers, a completely uniform construction capable of being technicallycontrolled is achieved with the fibers in the plastic 18 either beinghaphazardly arranged or oriented in a preselected manner. The hollowcellulose structure of the cellulose fiber or other equivalent fiber issignificant from the viewpoint of the present invention in that itprovides the exposed bottom surface 22 of the ski with a microporouscharacteristic which aids in the adherence of wax. When the hollowfibers are impregnated with the synthetic resin which is then cured toform a plate which is fixed to the bottom surface of the strip 10, withpressure being applied usually simultaneously with the curing, a slidingbottom ski surface is achieved where this latter surface has acombination of different materials with the proportions of the fibersand resin being capable of exact determination as, for example, byadjusting the pressure applied during the simultaneous pressing andcuring of the layer 16.

One of the important features of the present invention resides in thefact that the bottom surface 22 is ground or otherwise machined so thatthe sealed surface which results from the pressing is broken up tocreate the microporous surface where the passages 24 of the fibers 20flush with the surface 22 are open at the surface 22.

As a further feature of the present invention it is preferred to providea bottom layer 16 which has a thickness on the order of 0.5-1 mm, so asto achieve the additional advantage of eliminating scratches or otherdamage to the bottom surface by an equalizing grinding operation appliedto the bottom surface 22 after it has become excessively scratched orotherwise damaged during use. Inasmuch as the entire bottom layer 16 isof a homogeneous construction throughout its thickness, any machinedsurface 22 provided even subsequent to extensive use of the ski willhave the abovedescribed characteristics of the invention.

It is possible to regulate the characteristics of the surface 22, inaccordance with the invention, by varying the quantitative proportionsof fibers and resin as well as the hardness of the resin so as toachieve the best possible wear, sliding and waxing properties fordifferent conditions. It becomes possible, therefore, to produce fordifferent intended uses particular sliding bottom surfaces 22 which aremost appropriate for the intended purposes. For example a surface 22which has optimum sliding properties will be provided for skis to beused in contests, while maximum wear resistance will be provided foralpine skiing.

In addition, the hollow tubular fibers 20 have the effect of loweringthe thermal conductivity of the layer 16. This property is of greatsignificance because a low thermal conductivity improves the ease withwhich the surface 22 glides on extremely cold snow.

One example of the composition of the layer 16 which has proved to behighly successful for the bottom layer of a ski according to theinvention is the follow- The plastic 18 is an epoxy resin while thefibers are cellulose fibers, and the cellulose fibers constitute 50% byvolume while the epoxy resin 18 constitutes 45% by volume of the layer16. The remaining 5% by volume of the layer 16 is made up of fillers andpigments.

What is claimed is:

1. In a ski, an elongated narrow strip having one surface which isnormally directed upwardly to be engaged by a ski boot and an opposedsurface which is normally directed downwardly toward the ground, and abottom layer fixed to said strip and engaging and covering said opposedsurface thereof, said bottom layer being comprised for the most part ofa plastic material in which short tubular fibers are embedded withrandom orientations, said tubular fibers having internal capillarypassages and including at a surface of said bottom layer which isnormally directed downwardly away from said strip a number of fiberswhich are flush with and have their passages exposed at said surface ofsaid bottom layer to provide the latter surface with a microporousstructure.

2. The combination of claim 1 and wherein said plastic is athermosetting plastic.

3. The combination of claim 2 and wherein said fibers are cellulosefibers.

4. The combination of claim 3 and wherein said plastic is an epoxyresin.

5. The combination of claim 4 and wherein said cellulose fibers andepoxy resin respectively form 50% and 45% by volume of said bottom layerwhile the remainder thereof includes 5% by volume of fillers andpigments.

6. The combination of claim 5 and wherein said bottom layer has athickness on the order of 0.5-1 mm.

7. The combination of claim 1 and wherein said bottom layer has athickness on the order of 0.5-1 mm.

8. In a method of manufacturing a ski, the steps of applying to anormally downwardly directed bottom surface of a ski strip a layercomprised for the most part of plastic with short hollow tubular fibersembedded with random orientations therein, pressing said layer againstsaid strip with a given pressure while curing said layer to formtherefrom a plate which is fixed to said bottom surface of said strip,and then grinding a surface of said layer which is normally directeddownwardly away from said strip to expose the hollow interior of some ofthe fibers at the ground surface of said layer so as to provide thelatter surface thereof with a microporous structure.

9. In a method as recited in claim 8 and including the step ofregulating the pressure applied to said layer during curing thereof forcontrolling the proportions by volume of said plastic and fibers withrespect to each other.

1. In a ski, an elongated narrow strip having one surface which isnormally directed upwardly to be engaged by a ski boot and an opposedsurface which is normally directed downwardly toward the ground, and abottom layer fixed to said strip and engaging and covering said opposedsurface thereof, said bottom layer being comprised for the most part ofa plastic material in which short tubular fibers are embedded withrandom orientations, said tubular fibers having internal capillarypassages and including at a surface of said bottom layer which isnormally directed downwardly away from said strip a number of fiberswhich are flush with and have their passages exposed at said surface ofsaid bottom layer to provide the latter surface with a microporousstructure.
 2. The combination of claim 1 and wherein said plastic is athermosetting plastic.
 3. The combination of claim 2 and wherein saidfibers are cellulose fibers.
 4. The combination of claim 3 and whereinsaid plastic is an epoxy resin.
 5. The combination of claim 4 andwherein said cellulose fibers and epoxy resin respectively form 50% and45% by volume of said bottom layer while the remainder thereof includes5% by volume of fillers and pigmEnts.
 6. The combination of claim 5 andwherein said bottom layer has a thickness on the order of 0.5-1 mm. 7.The combination of claim 1 and wherein said bottom layer has a thicknesson the order of 0.5-1 mm.
 8. In a method of manufacturing a ski, thesteps of applying to a normally downwardly directed bottom surface of aski strip a layer comprised for the most part of plastic with shorthollow tubular fibers embedded with random orientations therein,pressing said layer against said strip with a given pressure whilecuring said layer to form therefrom a plate which is fixed to saidbottom surface of said strip, and then grinding a surface of said layerwhich is normally directed downwardly away from said strip to expose thehollow interior of some of the fibers at the ground surface of saidlayer so as to provide the latter surface thereof with a microporousstructure.
 9. In a method as recited in claim 8 and including the stepof regulating the pressure applied to said layer during curing thereoffor controlling the proportions by volume of said plastic and fiberswith respect to each other.